Alloy



Patented June 26, 1934 UNITED STATES ALLOY Bertrand S. Summers, Detroit, Mich., assignor to Michigan Steel Casting Company, a corporation of Michigan No Drawing. Application July 11, 1931 Serial No. 550,192

7 Claims.

My invention relates primarily to the manufacture of heat and corrosion resisting alloys containing as primary ingredients chromium and iron and it has particular relation to alloys of the above indicated character adapted for use in apparatus for the manufacture of paper pulp or car.-

bonizing boxes and apparatus used in the metallurgical treatment of iron and steel articles.

Specific uses of my'improved alloys are described 10 and claimed in my co-pending applications, Serial Nos. 550,193 and 550,194, both filed of even date herewith.

The invention has for its main objects the provision of an alloy which is highly resistant to attacks of sulphurous acid liquors; the provision of an alloy which is highly resistant to attacks of dilute sulphuric acid liquors; the provision of an alloy which is highly resistant to attacks of gases existing in heat treating furnaces; the provision of an alloy which does not check, crack, or blister under the influence of the conditions to which it is subjected in heat treating furnaces; the provision of an alloy in which grain growth is substantially inhibited; the provision of an alloy of the above indicated character which may be manufactured at a minimum of expense; the provision of an alloy which is comparatively tough and which may still machine with comparative ease; the provision of an alloy which is highly 30 resistant to oxidation at relatively high temperature.

It has heretofore been observed that certain alloys of chromium, iron and copper were comparatively resistant to attacks of atmospheric oxygen and similar weathering agencies. However, it has been found that such alloys as heretofore prepared offer but slight resistance to corrosion by such acids as sulphuric acid and hydrochloric acid, even when relatively dilute, and even such weak acids as acetic acid are known to attack it. It has also beenobserved that these alloys have a grain structure of relatively large size and for that reason are objectionable in certain uses. Also where subjected to relatively high temperature, for example, those existing in metallurgical furnaces employed in carbonizing iron and steel, the alloys tended to crack and blister and within a comparatively short period of time carbonizing' boxes and other articles formed therefrom are rendered completely useless. Furthermore, in case the copper content is raised much above the saturation point, the alloy blisters when subjected to high temperatures in the presence of oxygen.

This invention comprises the discovery that when certain metals are incorporated in proper proportionsinto an alloy containing iron and chromium as primary ingredients the objectionable features above indicated are substantially c0 overcome and a material which is highly useful larly useful in the manufacture of apparatus for making paper pulp prepared by the so-called sulphite process in which lime or lime stone is treated with sulphurous acid to form calcium and magnesium bisulphite, together with free sulphurous acid. This material when hot is highly corrosive in its action and for that reason alloys of chromium and iron as heretofore proposed are of little value for use in apparatus in contact therewith.

In the manufacture of this sulphurous acid resisting material, it is highly essential that the percentage of copper be controlled with considerable accuracy. Optimum results are obtained where approximately 3 per cent of copper is employed. The percentage of copper should not be reduced below approximately 2 per cent nor should it be increased materially above 5 per cent. Percentages of copper less than 2 per cent are not effective in preventing corrosion and at percentages somewhere between 3 and 4 percent the copper apparently begins to segregate from the other constituents of the alloy. So long as the percentage of copper is below approximately 5 per cent the segregated material is extremely finely and evenly distributed in the main body of the metal and the resistance of the latter to corrosive action of sulphurous acid liquors is not materially impaired. However, if the percentage of copper is increased appreciably beyond 5 per cent the bodies of segregated copper increase greatly in size and in such conditions they offer little more resistance to the corrosive action of sulphurous acid than copper entirely free from iron and chromium.

As previously indicated, the percentage of chromium in the alloy may vary over a range of approximately 15 to 30 per cent. However, by actual experience it is found that optimum results are obtained by use of approximately 20 per cent of chromium. Iron, together with certain other elements mentioned, may constitute the remainder of the alloy. However, if desired, 1 to 3 per cent of the iron may be replaced by molybdenum which toughens the metal and also materially increases resistance to corrosion by both sulphuric acid and sulphurous acid liquors. H

A small percentage to 2 per cent) of lead may also be incorporated into the alloy, with or without the molybdenum, and apparently results in a reduction of the size of the grains and grain boundaries and also retards or prevents grain growth where the alloy is employed in articles such as carbonizing boxes which are subjected to relatively high temperatures and subsequent cooling. The tendency of the alloy-to crack and blister in heat treating processes is thus materially reduced. The lead is further desirable in the alloy because it renders the alloy more workable and more resistant to corrosion.

Lead is a very difficult ingredient to incorporate into iron alloys. It readily oxidizes and in that condition readily volatilizes. It therefore must be added in about double the amount which is desired in the alloy. It may be added at the furnace just before the tap, or it may be flocculated by pouring a thin stream of molten lead into cold water. This so-called fiocculate can then be gradually added to the ladle or shank and. stirred While the addition is being made. In this way about 50% of the addition may be introduced in solid solution in the metal. The effect of this addition is most marked on the structure, and the properties of the metal, and it is this addition of lead to the iron chromium or iron-chromiumcopper alloy that makes an alloy effective for heat treating containers or apparatus.

My improved alloys containing iron, chromium and copper because of their great resistance to corrosion by sulphite liquors or sulphate liquors.

in the Kraft process of making paper and further because of the relatively low cost at which they may be manufactured and the ease with which they may be machined and worked, are particularly applicable as substitutes for certain nickel chromium alloys which are now employed as resistors of corrosion of sulphite liquors in the paper industry. The latter alloys are relatively expensive and are also very difiicult to machine and work.

As another feature of my invention, my alloys when lead is incorporated therein, as previously indicated, are particularly desirable for use in the manufacture of heat treating boxes such as carbonizing boxes employed in case hardening steel or iron. These boxes in actual practice are filled with a mixture of some suitable carbonaceous material and barium or other carbonates in which the articles to be treated are embedded. The boxes are then sealed to the entrance of air and are subjected to temperatures of 1500 to 1800 degrees Fahrenheit. Ordinary iron-chromium alloys containing no lead under these conditions fail within a short period notably because of the excessive growth of the grain structure therein.

-However, alloys prepared in accordance with the present specification and containing to 2 per cent of lead successfully withstands the high temperatures without any grain growth and resultant failure from cracking and blistering for a period of 1500 to 3000 hours.

Percentages of 2 to 5 per cent of copper are desirable in the alloys employed in the construction of carbonizing boxes because the copper increases the toughness and machinability of the alloy. However, the lead alone is quite efficient in reducing growth of the crystalline structure and for that reason it may under certain conditions be desirable to form the carbonizing boxes of an alloy containing chromium, iron and lead without the inclusion of copper.

The alloy when used for the manufacture of heat resistant articles is appreciably toughened by the addition of 1 to 3 per cent of molybdenum.

This metal increases the toughness of the alloy and also increases resistance to the corrosive action of oxygen and carbon-monoxide, the latter of which is generated in the heat treating furnace by combustion of fuel oils and also by reason of the action of oxygen in connection with the carbonizing boxes upon the carbonizing material contained therein.

Use of the metal is not limited to carbonizing boxes but extends to other relations such as the formation of structural elements for various types of furnaces and similar purposes where resistance to heat and/or corrosion is desirable.

A specific example of an alloy which may be used either as a sulphite liquor resisting agent or as a material for use in the construction of heat treating apparatus may be prepared in accordance with the following formula. Chromium approximately 20%; copper approximately 3%; lead to 2%; molybdenum 1% to 3%; iron the remainder. The term iron as herein employed designates the commercial product which may contain for instance to 1 4% of manganese, .2 to .7 of silicon and .1 to .4 percent of carbon. As previously indicated, the percentages of the different ingredients in the above indicated formula may be varied within certain limits without excessive impairment of the utility of the I alloys manufactured in accordance with the provisions of my invention are highly resistant to corrosion, particularly by certain agents such as carbon-monoxide, atmospheric oxygen and sulphite liquors. The grain thereof is also quite fine and the materials may be machined with readiness. The materials are quite resistant to grain growth and the resulting failure under high temperatures. alloys are highly desirable for commercial use in many arts of which the sulphite paper industry and the treatment of metal merely constitute two specific examples. a

Although I have described only the preferred embodiments of my invention,it is to be understood that the latter is not limited to these specific forms but that various modifications may be made For these reasons my improved therein without departure from the spirit of the invention or the scope of the appended claims.

I claim:

1. An alloy comprising 15 to 30 per cent chromium, A,; to 2 per cent lead, and the remainder being substantially iron.

2. A ferrous alloy consisting of 15 to 30 per cent cent chromium, .to 2 per cent lead, 1 to 3 per cent molybdenum, and the remainder iron.

6. A ferrous alloy consisting of 15 to 30 per cent chromium, to 2 per cent lead, 2 to 5 per cent copper, 1 to 3 per cent molybdenum, and the remainder iron.

7. A ferrous alloy consisting of about 20 per cent chromium, to 2 per cent lead, about 3 per cent copper, 1 to 3 per cent molybdenum, and the remainder iron.

' BERTRAND S. SUMMERS. 

